High performance windows with new glazing technologies not only reduce energy costs but make homes more comfortable as well.
During cold weather, exterior temperatures drive interior glass surface temperatures down below the room air temperature; how low the glass temperature drops depends on the window's insulating quality. If people are exposed to the effects of a cold surface, they can experience significant radiant heat loss to that cold surface and they feel uncomfortable, even if the room air temperature is comfortable.
When the interior glass surface temperature is 52°F or less, it is most likely that there will be discomfort.
During warm weather, solar radiation can cause discomfort. Just as people turn up the heat to compensate for cold windows in cold weather, they may use air-conditioning to counter the effects of warm window surfaces and sunlight in summer.

Winter Thermal Comfort

An older window with a lower glass
temperature feels colder because more heat is radiated from a person's body to
the window. Cold glass can also create uncomfortable drafts as air next to the
window is cooled and drops to the floor. This sets up an air movement pattern
that feels drafty and accelerates heat loss. High performance windows with lower U-factors will result in a higher interior
window temperature in winter and thus greater comfort. Proper installation along
with weatherstripping designed to seal tightly (for operable windows) will also
improve comfort by reducing cold air leakage.